High efficiency and fast response AC-DC voltage converters

ABSTRACT

The present invention discloses circuits and methods for high efficiency and fast response AC-DC voltage converters. In one embodiment, an AC-DC voltage converter can include: (i) a first stage voltage converter having an isolated topology with a power factor correction function, where the first stage voltage converter is configured to convert an AC input voltage to a series-connected N branches of first stage voltages, where N is a positive integer of at least two; (ii) a second stage voltage converter having a non-isolated topology, where the second stage voltage converter is configured to convert one of the N branches of the first stage voltages to a second stage voltage; and (iii) where the second stage voltage and a remaining of the N branches of the first stage voltages are configured to be series-connected and converted to a DC output voltage.

RELATED APPLICATIONS

This application claims the benefit of Chinese Patent Application No.201210188848.2, filed on Jun. 6, 2012, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the field of switch mode powersupplies, and more specifically to high efficiency and fast responseAC-DC voltage converters.

BACKGROUND

AC-DC converters are typically used in various electronics devices toconvert an AC voltage level to one or more regulated DC voltage levels.Such converters may utilize power factor correction (PFC) and/orpulse-width modulation (PWM) circuitry in order to control the regulatedlevels, and to improve the conversion efficiency. Among the concerns inAC-DC voltage converter designs are circuit power losses, transmissionefficiency, overall product costs, circuit volume, and regulationprecision.

SUMMARY

Particular embodiments can provide high efficiency and fast responseAC-DC voltage converters.

In one embodiment, an AC-DC voltage converter configured to convert anAC input voltage to a DC output voltage, can include: (i) a first stagevoltage converter having an isolated topology with a power factorcorrection function, where the first stage voltage converter isconfigured to convert the AC input voltage to a series-connected Nbranches of first stage voltages, where N is a positive integer of atleast two; (ii) a second stage voltage converter having a non-isolatedtopology, where the second stage voltage converter is configured toconvert one of the N branches of the first stage voltages to a secondstage voltage; and (iii) where the second stage voltage and a remainingof the N branches of the first stage voltages are configured to beseries-connected and converted to the DC output voltage at an outputterminal of the AC-DC voltage converter.

Embodiments of the present invention can advantageously provide severaladvantages over conventional approaches. For example, a second stagevoltage converter may only need to convert part of an output voltage ofa first stage voltage converter, so as to reduce overall circuit powerlosses and improve transmission efficiency. In addition, switches withrelatively lower withstand voltages and smaller volumes can be utilizedto reduce product costs and circuit volume. Other advantages of thepresent invention may become readily apparent from the detaileddescription of preferred embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example two-stage AC-DC voltageconverter.

FIG. 2 is a block diagram of another example two-stage AC-DC voltageconverter.

FIG. 3 is a block diagram of a first example AC-DC voltage converter inaccordance with embodiments of the present invention.

FIG. 4 is a block diagram of a second example AC-DC voltage converter inaccordance with embodiments of the present invention.

FIG. 5 is a block diagram of a third example AC-DC voltage converter inaccordance with embodiments of the present invention.

DETAILED DESCRIPTION

Reference may now be made in detail to particular embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention may be described in conjunction with thepreferred embodiments, it may be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents that may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set fourth in order to provide a thoroughunderstanding of the present invention. However, it may be readilyapparent to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knownmethods, procedures, processes, components, structures, and circuitshave not been described in detail so as not to unnecessarily obscureaspects of the present invention.

As shown in FIG. 1, an example two-stage structure used in AC-DC voltageconverters can include a power factor correction (PFC) control circuit102, pulse-width modulation (PWM) control circuit 104, optical coupler106, and an isolated DC-DC converter. This “isolation” refers to theexistence of an electrical harrier between the input and output of theDC-DC converter. The simplest example of a “non-isolated” converter is athree terminal linear regulator, where one terminal is used for andunregulated input, one terminal is used for the regulated output, andone terminal is for the common.

In this example, PFC control circuit 102 can be used to improve thepower factor and the latter stage flyback converter can be used totransfer an output voltage of the first stage to the secondary-sidethrough an isolated topology. However, with this topology, diode D₁,switch Q₁, switch Q₂, and capacitor C₁ should utilize devices with ahigh breakdown or “withstand” voltage. In addition, the overall productcosts may be increased, and the circuit response may be slowed due tooptical coupler 106.

To overcome the disadvantages of the topology shown in FIG. 1, theexample structure of FIG. 2 can be utilized. The structure of FIG. 2 canachieve power factor correction (e.g., via PFC control circuit 102), andmay generate DC voltage V_(out1) by using a flyback converter. Also, anon-isolated DC-DC converter can be used in the second stage circuit toconvert DC voltage V_(out1) to output voltage V_(out). As compared tothe circuit structure shown in FIG. 1, the structure of FIG. 2 mayfacilitate integration with only one high withstand voltage switch.Also, primary-side control applied without an optical coupler can reducethe overall product costs. However, drawbacks of this structure caninclude a second stage circuit that regulates the output voltage of thefirst stage circuit, possibly resulting in unnecessary power losses.

In particular embodiments, a high efficiency, fast response AC-DCvoltage converter can include a two-stage structure to convert an ACinput voltage to a constant DC output voltage, where the second stagevoltage converter may only convert part of the output voltage of thefirst stage voltage converter. In this way, overall circuit power lossescan be reduced, and the transmission efficiency can be improved. Inaddition, switches in the second stage voltage converter may only bear aportion of the output voltage of the first stage voltage converter,rather than the entire output voltage. Thus, switches with relativelylower withstand voltages and smaller volumes can be utilized in order toreduce product costs and circuit volume. Further, a control method ofthe second stage voltage converter can be a PWM control method with arelatively faster regulating speed. Also, the control circuit canreceive the entire DC output voltage of the AC-DC voltage converter,rather than the output voltage of the second stage voltage converter, asfeedback information. In this way, relatively fast and preciseregulation of the output voltage of the entire converter can beachieved.

In one embodiment, an AC-DC voltage converter configured to convert anAC input voltage to a DC output voltage, can include: (i) a first stagevoltage converter having an isolated topology with a power factorcorrection function, where the first stage voltage converter isconfigured to convert the AC input voltage to a series-connected Nbranches of first stage voltages, where N is a positive integer of atleast two; (ii) a second stage voltage converter having a non-isolatedtopology, where the second stage voltage converter is configured toconvert one of the N branches of the first stage voltages to a secondstage voltage; and (iii) where the second stage voltage and a remainingof the N branches of the first stage voltages are configured to beseries-connected and converted to the DC output voltage at an outputterminal of the AC-DC voltage converter.

Referring now to FIG. 3, shown is a first example AC-DC voltageconverter in accordance with embodiments of the present invention. Inthis example, the AC-DC voltage converter used to convert an AC inputvoltage to a DC output voltage can include a first voltage converter 302and a second voltage converter 304. In particular, the first voltageconverter 302 can utilize an isolated topology with a function of powerfactor correction to convert the AC input voltage to a series-connectedN branches of first stage voltages V_(bus1), V_(bus2), . . . V_(busn).For example, N can be a positive integer of at least two (e.g., 2, 3, 4,etc.).

The second voltage converter 304 can utilize non-isolated topology toone of the first stage voltages (e.g., V_(bus2)) to second stage voltageV₂. Also, the second stage voltage (e.g., V₂) can be series-connectedwith the remaining (N−1) branches of the first stage voltages. In thisway, DC output voltage V_(o) can be generated at an output terminal ofthe AC-DC voltage converter. For example, DC output voltage V_(o) may bea sum of the second stage voltage (e.g., V₂) and the remaining (N−1)branches of the first stage voltages (e.g., V_(bus1), V_(bus3), . . .V_(busn)). In particular embodiments, second stage voltage converter 304of the AC-DC voltage converter may only need to convert part or one(e.g., V_(bus2)) of the series-connected output voltages of the firststage voltage converter. In this fashion, overall power losses can bereduced to improve conversion efficiency.

Referring now to FIG. 4, shown is a second example AC-DC voltageconverter in accordance with embodiments of the present invention. Inthis example, the first stage voltage converter can output two branchesof first stage voltages (e.g., V_(bus1) and V_(bus2)). Thus in thiscase, N=2 in this specific implementation of the AC-DC voltageconverter. The first stage voltage converter can include a rectifierbridge, a flyback converter with two output channels, and power factorconnection (PFC) control circuit 402.

The rectifier bridge can be used to convert the AC input voltage to a DCvoltage, and may include electromagnetic interference (EMI) reductioncircuitry. The flyback converter can connect with the rectifier bridgeto receive the DC voltage, and to convert the DC voltage toseries-connected first stage voltages V_(bus1) and V_(bus2). Forexample, PFC control circuit 402 can utilize a quasi-resonance method tocontrol primary-side switch Q₁, so as to maintain the input voltage ofthe flyback converter as in phase with the input current.

In particular embodiments, the topology of the second stage voltageconverter can be a non-isolated buck regulator that includes switch Q₂,switch Q₃, inductor L₁, and output capacitor C_(out). The second stagevoltage converter can receive first stage voltage V_(bus1) output by thefirst stage voltage converter, and convert V_(bus1) to second stagevoltage V₁ using PWM control circuit 404. Series-connected second stagevoltage V₁ and first stage voltage V_(bus2) can be configured as outputvoltage V_(o) of the AC-DC voltage converter.

The PWM control circuit can receive output voltage V_(o) of the AC-DCvoltage converter, and generate a PWM signal to control the duty cyclesof switches Q₂ and Q₃ of the second stage voltage converter. In thisparticular example, because the switches in the second stage voltageconverter may only bear a portion (e.g., V_(bus1)) of the output voltageof the first stage voltage converter, rather than the entire outputvoltage, switches Q₂ and Q₃ may have relatively low withstand voltageand relatively smaller volume. Thus, the product costs and circuitvolume can be reduced.

Also, a control method of the second stage voltage converter can includea PWM control method that has a relatively fast regulating speed. Inaddition, the PWM control circuit can receive the full DC output voltageV_(o) of the AC-DC voltage converter, instead of output voltage V₁ ofthe second stage voltage converter, as feedback information. In thisway, output voltage V_(o) of the entire converter can be regulated withincreased speed and precision.

Referring now to FIG. 5, shown is a block diagram of a third exampleAC-DC voltage converter in accordance with embodiments of the presentinvention. As compared to the example shown in FIG. 4, the multi-outputisolated converter in the first stage voltage converter can include aforward converter. The first stage voltage converter can include arectifier bridge, EMI reduction circuitry, a forward converter with twooutput channels, and PFC control circuit 502.

Also, a topology of the second stage voltage converter can include anon-isolated boost converter formed by switch Q₄, inductor L₂, diode D₂,and output capacitor C_(out2). The specific working principle may be thesame or similar to the example shown in FIG. 4. The forward convertercan utilize a primary-side control method, where the operation state ofthe forward converter can be controlled by detecting the output voltageof the auxiliary winding.

The second stage voltage converter can be any appropriate non-isolatedtopology (e.g., non-isolated boost regulator, buck regulator, boost-buckregulator, etc.). For example, the second stage voltage converter shownin FIG. 4 can also be a non-synchronous buck regulator, and the secondstage voltage converter shown in FIG. 5 can accordingly be a synchronousboost regulator. Thus, any suitable converters can be utilized inaccordance with embodiments of the present invention.

The above has described some example embodiments of the presentinvention, but practitioners with ordinary skill in the art will alsorecognize that other techniques or circuit structures can also beapplied in accordance with embodiments of the present invention. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and theirequivalents.

What is claimed is:
 1. An AC-DC voltage converter configured to convertan AC input voltage to a DC output voltage, the AC-DC voltage convertercomprising: a) a first stage voltage converter having an isolatedtopology with a power factor correction function, wherein said firststage voltage converter is configured to convert said AC input voltageto a series-connected N branches of first stage voltages, wherein N is apositive integer of at least two; b) a second stage voltage converterhaving a non-isolated topology, wherein said second stage voltageconverter is configured to convert one of said N branches of said firststage voltages to a second stage voltage; and c) wherein said secondstage voltage and a remaining of said N branches of said first stagevoltages are configured to be series-connected and converted to said DCoutput voltage at an output terminal of said AC-DC voltage converter. 2.The AC-DC voltage converter of claim 1, wherein said second stagevoltage converter comprises a pulse-width modulation (PWM) controlcircuit configured to receive said DC output voltage, and to generate aPWM signal configured to control duty cycles of switches in said secondstage voltage converter to convert said one branch of said first stagevoltages to said second stage voltage.
 3. The AC-DC voltage converter ofclaim 1, wherein said first stage voltage converter comprises: a) arectifier bridge configured to convert said AC input voltage to a DCinput voltage; b) a multi-output isolated converter coupled to saidrectifier bridge, wherein said multi-output isolated converter isconfigured to convert said DC input voltage to said series-connected Nbranches of said first stage voltages; and c) a power factor correction(PFC) control circuit configured to maintain said DC input voltage in asame phase as an input current of said PFC control circuit.
 4. The AC-DCvoltage converter of claim 3, wherein said multi-output isolatedconverter comprises one of: a forward converter and a flyback converter.5. The AC-DC voltage converter of claim 3, wherein said multi-outputisolated converter is controllable by a primary-side control method bydetecting an auxiliary voltage of an auxiliary winding of saidmulti-output isolated converter.
 6. The AC-DC voltage converter of claim3, wherein said PFC control circuit is configured to utilize aquasi-resonance control method to control a primary-side switch.
 7. TheAC-DC voltage converter of claim 1, wherein said non-isolated topologyof said second stage voltage converter comprises at least one of: anon-isolated buck regulator, a non-isolated boost regulator, and anon-isolated boost-buck regulator.